We demonstrate maskless lithography fabrication of nanolayered heterostructured hybrid plasmonic waveguides. This includes the measured optical properties of pulsed magnetron sputtered 15 nm films of aluminum oxide and aluminum nitride. Hybrid plasmonic waveguides, where the modes highest intensity is largely confined to the thin aluminum oxide layer, were constructed by maskless lithography using an aperture-type near-field scanning optical microscope.

The current state of energy is characterized by complex challenges in production processes and environmental issues. With the world population continuing to multiply faster and the globalization process, additional energy production is needed to meet future demands. Solar energy is one of the best sustainable energy resources, which is expected to play a vital role in this scenario. One of the best techniques to harvest this resource is through solar photovoltaic technology, which produces electricity directly from solar radiation. But, one of the problems still persisting is its low efficiency. To harness this technology, this problem needs to be addressed. Metamaterial (MTM) technology has enabled the creation of advanced devices for various applications. Solar cell technology is one of the fields to benefit from this technology. MTM perfect absorber can be used in solar cells to improve their absorption. Multiple-bands MTM absorber for next generation high-efficiency solar cells is proposed. The design gives a nearly perfect absorption (99.94%) with a bandwidth of 23.4% in visible spectrum. In addition, the geometric flexibility of a proposed design causes its absorption rate to be insensitive of polarization angles and angles of incident electromagnetic radiations.

We focused on the effects of group-velocity dispersion (GVD) on the coherent pulse progression in midinfrared quantum-cascade lasers (QCLs). We carried out the study on Fabry–Perot (FP) cavities. Comparison of GVD effects on the two kinds of typical QCL cavities, i.e., FP and ring cavities, brings insight into the interaction between the GVD and spatial hole burning (SHB) effect, which is only supported by FP cavities but not ring cavities. The theoretical model is built based on the Maxwell–Bloch formulism accounting for two-way propagations of electric field and polarization as well as the couplings among the electric field, polarization, and population inversion. The pulse evolution in time–spatial domains is simulated by the finite-difference method with prior nondimensionalization, which is necessary for a convergent solution. Results predict that the SHB could broaden the QCL gain bandwidth and induce additional side modes closely around the central lasing mode with an intensity more pronounced than that of GVD associated side modes. Moreover, owing to the SHB, the lasing instability caused by GVD is weaker in an FP cavity than a ring cavity.

Design and analysis of a graphene-based suspended nanostrip line for integrated circuit applications at terahertz (THz) frequencies are presented. A suspended nanostrip waveguide structure has been analyzed using a full wave electromagnetic (EM) simulator to obtain its transmission line characteristics, such as propagation constant and characteristic impedance. Closed form expressions have been developed for the same. Later, graphene-based plasmonic resonators have been analyzed. Coupled resonators have been used to implement a filter-based diplexer. A split ring resonator has been used to design a sensor for measuring refractive index variation. The transmission spectra of the designed graphene-based SRR have been discussed in detail with the help of full-wave EM simulation tools, providing a vivid vision of the sensing potential of the proposed sensor structure. The simulation results depict two surface plasmon resonance peaks in the transmission spectrum, showing a linear relationship with the dielectric constant of the material under sensing. The tuning capability of the graphene tunable sensor allows its usage in the field of nanodevices and sensor applications.

Electromagnetic (EM) behaviors of photonic crystals (PhCs) and nanoantenna (NA) arrays have been extensively studied and applied to a myriad of applications, including light absorption, surface-enhanced Raman scattering, light trapping in photovoltaics, and spectral narrowing of thermal emission. However, not many works have studied the integration of three-dimensional (3-D) PhCs and NA arrays into one structure mainly due to technical challenges in manufacturing 3-D PhCs. The present article reports the design analysis of a hybrid optical structure that has a gold rectangular NA array aligned on a 3-D silicon-on-nothing (SON) PhC substrate. By applying a continuous phase field model, we numerically simulate the formation of SON-PhC structures (i.e., a 3-D periodic array of spherical voids in silicon) during the high-temperature annealing process of a silicon substrate having vertical trenches. Photonic behaviors of the NA-on-SON PhC structure are computed using the finite-difference time-domain method. The obtained results exhibit the resonant absorption of midinfrared (mid-IR) light in the stopping bands of the SON-PhC (3.0  μm  <  λ  <  7.5  μm) by photon coupling with the free electron oscillations in each NA structure. This PhC-mediated NA resonance is manifested by highly concentrated electric fields at NA corners; the corresponding local field enhancement factor is one order of magnitude greater than that of the NA array on a bare silicon substrate.

Quantum dot base infrared detectors have many advantages such as lower dark current, higher operating temperature, higher photoconductive gain, and broader infrared response. For this reason, we have studied a pyramidal shape quantum-dot infrared photodetector (QDIP) in which the different mechanisms of noise and dark current, the effects of QD size variation, the temperature, and applied electric field are considered. Self-assembled In0.3Ga0.7As  /  GaAs pyramidal shape quantum dots have been considered and optical properties in the conduction band using effective mass Schrodinger equation by the finite-difference time-domain (FDTD) method have been analyzed. Finally, the detectivity calculated as functions of the applied electrical field and temperature. For example, at the T  =  77  °  K and E  =  2  kV  /  cm, the detectivity is 3  ×  1013  cmHz  −  1/2  /  W.

We report a simultaneous amplified emission from InAs-based self-assembled quantum dot and quantum well in a multistack dot-in-a-well superluminescent light-emitting diode (SLD) for application in broadband sources. A combination of atomic force microscopy, photoluminescence of the test structures, and optoelectronic characterization of SLD is used to obtain an emission bandwidth of ∼292  nm covering O–S communication band (including 850-nm band) and a maximum continuous power of ∼1.33  mW at room temperature.

Y₂O₃ nanocrystalline phosphors doped with Er^3  +  /  Yb^3  +  /  Tm^3  + ions were prepared using thermal decomposition technique at 500°C. Pure cubic phase of Y₂O₃ with an average crystallite size ∼29  ±  4  nm was determined from x-ray diffraction and high-resolution transmission electron microscope measurements. Their upconversion luminescence spectra were measured under 975-nm laser diode excitation at room temperature. A bright blue emission was simultaneously observed at 480 nm due to the G₄1  →  H₆3 transition of Tm^3  + ions, with the green (550 nm) and red (670 nm) emissions due to the H_11/22, S_3/24  →  I_15/24 and F_9/24  →  I_15/24 transitions of Er^3  + ions, respectively. Relative emission intensities of these colors were significantly affected by the Er^3  + concentration as well as the excitation power density of 975-nm laser light. Color quality parameters and the color tuning abilities were determined from the Commission International de I’Echairage 1931 chromaticity diagram analysis, color rendering index, and their correlated color temperature values. A careful color tuning from cool to warm white light in Y₂O₃  :  Er^3  +  /  Yb^3  +  /  Tm^3  + phosphors was achieved by controlling both the doping concentration of Er^3  + ions and the excitation power density of the 975-nm laser light.

The modal analysis of a lossy coupled plasmonic waveguide consisting of two graphene sheets sandwiched among three SiO₂ layers is presented. This analysis extracts even and odd complex propagation constants in addition to even and odd characteristic impedances at various Fermi levels. It is shown that the first even mode is lossless in theory, but other modes are very lossy. Taking into account the losses, first, the transmission line (RLCG) model, including self and mutual elements, is constructed for various Fermi levels and frequencies. Then, the length of a lossy plasmonic directional coupler based on the coupled plasmonic waveguide is designed for a variety of Fermi levels. The transmission, reflection, coupling, and isolation coefficients of the device are obtained using advanced design system for several Fermi levels and coupler lengths to maximize the power at the coupled ports and minimize it on the reflected and isolated ports. The computational results show that the minimum length of the plasmonic coupler is 39 nm at 40 THz. Sensitivity analysis shows that increasing the frequency, decreases the length of the optimum device while increasing the sheets’ Fermi level. Finally, Comsol simulations of the coupled plasmonic waveguide are utilized to verify the even and odd modes.

The deficiency for quantum dots (QDs) used as optical amplified medium (such as QD-doped fibers) is nonradiative Auger recombination based on multiple exciton state, which is related to pump power, pump frequency, and pump wavelength. Thus, the Auger recombination lifetime was introduced in the existing three-level system, further the emission of PbSe QD-doped optical fiber as a function of pump parameters mentioned above was simulated in order to maximize emission intensity and optical gain. The emission intensity increased first and then saturated with the pump power, showing good agreement with the experimental data. An optimal pump power maximizing the emission intensity was observed, which is distinguished from the non-Auger decay-result that the emission intensity increased with the pump power in a linear way. The emission intensity increased with the increasing pump frequency (from 4 to 10  ×  10⁴  Hz). In addition, 532-nm pump light was confirmed to enhance the output intensity compared to the other longer wavelengths. The relationship between emission intensity and pump fluence is similar to that of the experimental data. The maximal optical gain of 11.5 dB was obtained. The threshold pump power decreased with the increasing pump frequency, in which situation, larger pump power was needed to achieve the optical gain saturation. This research might be a theoretical basis for QD-doped optical fiber amplifiers and lasers.

We show a unique design of teepee-like photonic crystal (TP-PC) structure that possesses a true gradient, Gaussian-type surface profile for smooth and accurate index matching between air and silicon for near-perfect light trapping. Such funnel-like, inverse-conical topography is capable of achieving near-zero optical reflection and near-unity solar absorption with excellent angular response over the entire visible light wavelength range. The fabrication only requires standard microelectronics reactive-ion etching (RIE) process. We demonstrate how various process parameters, such as RIE gas mixture ratio, RIE power, thickness of silicon dioxide (SiO₂) coatings, and lattice constant of the photonic crystal, can impact the details of the “Gaussian” profile and further improve the optical performance of the TP-PC structure at broad-λ, broad-θ, especially in the ultraviolet (UV) wavelength range. Our finite-difference time-domain (FDTD) simulation of the TP-PC structure reveals existence of multiple absorption resonances in the 800- to1100-nm wavelength range. Poynting vector plots show that such strong absorption enhancements at the resonant frequencies are due to long-lifetime photonic modes arising from parallel-to-interface refraction of the incoming sunlight and formation of vortex-like energy flow pattern inside the TP-PC structure. Our design will lead the way for future development of ultrathin, high-efficiency c-Si solar photovoltaics.

We report a numerical study of the effect of material dispersion on the omnidirectional reflectors (ODR) properties in the case of one-dimensional photonic crystal structures consisting of alternate layers of zinc oxide as material of high refractive index and SiO2 as material of low refractive index. The interplay of dispersion and structural parameters on the ODR properties of the structure of interest has been analyzed. Taking into account the material dispersion properties, shift in the wavelength range for ODR from (1079  −  1158  nm) to (1133  −  1103  nm) is observed. This shows the narrowing of the bandwidth for ODR from 79 to 30 nm as a result of material dispersion. The wavelength range of interest is close to optical communication wavelengths and is useful in many optical device applications.

It is shown that in the potential energy of an exciton of spatially separated electrons and holes [hole moves in the amount of quantum dots (QDs), the electron is localized on a spherical surface section (QD—dielectric matrix)], taking into account centrifugal, energy gives rise band of the quasistationary surface exciton states that with the increase of the radius of QD becomes stationary state. The mechanisms of formation of the spectra of interband and intraband absorption (emission) of light in nanosystems containing aluminum oxide QDs, placed in the matrix of vacuum oil, are presented. It is shown that the electron transitions in the area of the surface exciton states cause significant absorption in the visible and near-infrared wavelengths and cause the experimentally observed significant blurring of the absorption edge.

A cost-efficient fiber-optic strain and temperature sensor has been proposed and demonstrated experimentally. The sensor consists of a segment of polarization-maintaining fiber (PMF) and two segments of multimode fiber (MMF). Two segments of MMF, which are used as beam splitter and combiner, are embedded on both ends of the PMF. The all-fiber sensor is put in the middle of the single-mode fiber. Due to the ratio of the strain and temperature responses of the sensor, the measurement of strain and temperature can be achieved by monitoring the transmission spectrum. The experimental result shows that the strain sensitivity is up to −3.16  pm  /  μϵ in the range of 0 to 1000  μϵ and the temperature sensitivity is 0.071  nm  /    °  C in the range from 10°C to 45°C. This sensor exhibits the advantages of low cost and high sensitivity and may have potential application in strain and temperature measurement.

The helical nanowires of a chiral sculptured thin film (CSTF) were taken to be made from a weakly dissipative material while the void regions between nanowires were filled with an active material, and the planewave reflection/transmission characteristics were investigated numerically. The CSTF was found to simultaneously amplify left-circularly polarized incident light and attenuate right-circularly polarized incident light, or vice versa, depending upon its structural handedness. This polarization-state-dependent attenuation and amplification phenomenon is sensitive to the direction of incidence and the thickness of the CSTF. Furthermore, the presence of both dissipative and active materials allows the high reflectance to exceed unity across a substantial proportion of the circular Bragg spectral regime for incident light of one circular polarization state but not of the other circular polarization states. That is, the CSTF functions as a circular Bragg supermirror for one, and only one, circular polarization state.

The work demonstrates an electrospun nanocomposite of recombinant spider silk protein (rSSp) nanofibers with embedded cerium oxide (ceria) nanoparticles. RSSP (MaSp1) has been produced, extracted from goat milk, and fabricated into nanofibers using an electrospinning process. The resulting electrospun nanofibers have a mean diameter of ∼50  nm. Furthermore, ceria nanoparticles of mean diameter &lt;10  nm were added in the spinning dope to be embedded within the generated nanofibers. These nanoparticles show certain optical activity due to optical trivaliant cerium ions, associated with formed oxygen vacancies. The formed nanocomposite shows promising mechanical properties such as the Young’s modulus, elasticity (or elongation at break), and toughness. In addition, the electrospun mat becomes fluorescent with 520-nm emission upon exposure to UV light, due to excitation of the optically active ceria nanoparticles. Also, the formed nanocomposite shows a decay of its electric resistance over time upon exposure to cyclic loads at different humidity conditions. The synthesized nanocomposite can be utilized in different biomedical, textile, and sensing applications.

Midinfrared spectrum region has proved its great potential in various fields including security, medical examination, product inspection, and materials characterization. However, midinfrared detectors, one of the most important components, have not been fully developed and their performance can be much improved. In contrast to well-known nanostructured semiconductor detectors, graphene-based detectors are emerging and are proposed to tackle shortcomings of earlier detectors. Nevertheless, they still suffer from obstacles due to low light absorption originating from a single atomic layer. Recently, the introduction of plasmonic antennas is changing the situation and is attracting much interest. We present a midinfrared photodetector based on a multiresonant frequency bull’s eye antenna coupled with monolayer graphene. The bull’s eye antenna is one of the plasmonic antennas that can achieve high concentration of electric field and enhanced transmission of incident light. Though conventional bull’s eye antennas exhibit only single resonant frequency that restricts to a measured frequency range, we here designed and fabricated the bull’s eye antenna with wider band transmission so that various frequency regions can be studied with a single device. We demonstrated that the graphene device integrated with the multifrequency plasmonic antenna enabled the room-temperature midinfrared detection, together with the ability of frequency filtering in a desirable band. Our device design is also applicable to other frequency regions including visible light and terahertz waves by adjusting structural parameters.

The structural and luminescent results of nondoped, terbium and dysprosium doped, and codoped Y₂O₃ powders are presented. Different percentages of the rare earth ions were employed. The powders were obtained by means of the solvent evaporation technique and were annealed at 1100°C for 2 h. The emission spectra of these samples are associated with the characteristic intraelectronic energy levels that are related to the Tb^3  + and Dy^3  + ions transitions. The maximum peaks of emission are located at 542 nm with λ_exc  =  274  nm for terbium that is associated with the D5₄ to F7₅ transition; for dysprosium, the maximum is at 573 nm, when excited with λ_exc  =  210  nm, corresponding to the F4_{9  /  2} to H6_{13  /  2} transition; the emission spectra of the Y₂O₃  :  Tb4  %    :  Dy3  %   and Y₂O₃  :  Tb4  %    :  Dy0.75  %   phosphors were also obtained, and the emissions of these two ions are observed when excited with λ_exc  =  260  nm, suggesting that these ions are near neighbors, giving place to energy transfer between these two ions. When the sample of Y₂O₃  :  Tb_3  + is excited with λ_exc  =  274  nm, a single exponential decay is observed with τ  =  2.95  ms; when the Y₂O₃  :  Dy^3  + is excited with λ_exc  =  210  nm, there is decay time with τ  =  0.89  ms; and when excited with λ_exc  =  274  nm, the phosphors of Y₂O₃  :  Tb^3  +  :  Dy^3  + also have a single exponential decay with τ  =  2.04  ms. The Commission Internationale de l’Eclairage diagram coordinates obtained for different relative contents of these lanthanide ions are given. X-ray diffraction analyses of these phosphors indicate a polycrystalline cubic yttrium oxide structure with a grain size running from 37 to 45 nm.

The optical and structural characteristics of Y₂O₃ : Eu (III)-benzoate hybrid nanophosphors, synthesized by the microwave-assisted solvothermal technique, are reported in this work. Benzyl alcohol was used during the synthesis, carried out at low temperatures in the microwave reactor, to obtain the Y₂O₃ : Eu(III)-benzoate-layered hybrid nanophosphors. The benzyl alcohol led to the incorporation of benzene rings (belonging to benzoate group) around the Y₂O₃ : Eu(III) molecules, promoting a lamellar structure and showing the previously reported luminescent “antenna effect” in the nanophosphors. Y₂O₃ : Eu(III)-benzoate nanophosphors showed a high photoluminescence emission intensity at 590, 612, 650, and 697 nm due to the interelectronic D₀5 to F₁7, F₂7, F₃7, and F7₄ transitions of the europium ions. A stark split might be present due to the variation of the annealing temperature given to the Y₂O₃ : Eu(III)-benzoate nanophosphors. The nanostructured hybrids showed the appearance of complex morphologies similar to flower petals. The as-obtained nanophosphors were in the range of ∼20 nm and showed the reported x-ray diffraction reflections for these kinds of materials.

An economical way to extract semiconducting single-walled carbon nanotubes from common single-walled carbon nanotubes by the liquid-phase exfoliation method was demonstrated. Using the extracted samples as a saturable absorber, a passively Q-switched Nd  :  YVO₄ laser was realized, delivering a pulse duration of 83 ns at a repetition rate of 290 kHz, resulting in a maximum peak power of 1.3 W. Such an outstanding saturable absorption might be caused by high diameter concordance and semi-conducting property.